Abstract
Microcavities based on group-III nitride material offer a notable platform for the investigation of light-matter interactions as well as the development of devices such as high efficiency light emitting diodes (LEDs) and low-threshold nanolasers. Disk or tube geometries in particular are attractive for low-threshold lasing applications due to their ability to support high finesse whispering gallery modes (WGMs) and small modal volumes. In this article we present the fabrication of homogenous and dense arrays of axial InGaN/GaN nanotubes via a combination of displacement Talbot lithography (DTL) for patterning and inductively coupled plasma top-down dry-etching. Optical characterization highlights the homogeneous emission from nanotube structures. Power-dependent continuous excitation reveals a non-uniform light distribution within a single nanotube, with vertical confinement between the bottom and top facets, and radial confinement within the active region. Finite-difference time-domain simulations, taking into account the particular shape of the outer diameter, indicate that the cavity mode of a single nanotube has a mixed WGM-vertical Fabry-Perot mode (FPM) nature. Additional simulations demonstrate that the improvement of the shape symmetry and dimensions primarily influence the Q-factor of the WGMs whereas the position of the active region impacts the coupling efficiency with one or a family of vertical FPMs. These results show that regular arrays of axial InGaN/GaN nanotubes can be achieved via a low-cost, fast and large-scale process based on DTL and top-down etching. These techniques open a new perspective for cost effective fabrication of nano-LED and nano-laser structures along with bio-chemical sensing applications.
Highlights
III-Nitride micron and submicron cavities such as disks, rods, rings and tubes shaped structures, in which light can be confined around their periphery by total internal reflection [1,2], have been proposed as a way to overcome the difficulties of incorporating mirrors in vertical-cavity surface-emitting lasers [3,4]
Microcavities based on group-III nitride material offer a notable platform for the investigation of light-matter interactions as well as the development of devices such as high efficiency light emitting diodes (LEDs) and low-threshold nanolasers
Disk or tube geometries in particular are attractive for low-threshold lasing applications due to their ability to support high finesse whispering gallery modes (WGMs) and small modal volumes
Summary
III-Nitride micron and submicron cavities such as disks, rods, rings and tubes shaped structures, in which light can be confined around their periphery by total internal reflection [1,2], have been proposed as a way to overcome the difficulties of incorporating mirrors in vertical-cavity surface-emitting lasers [3,4]. High-aspect-ratio axial tubular cavities fabricated from planar LED structures by top-down etching, with the active region decoupled from the underlying planar buffer layer, provide the opportunity to fabricate electrically injected nano-lasers and photonic-electronic integrated circuits, independently of the nature of the substrate, which could even be visible light absorbing silicon. The use of DTL enables the realization of an homogenous array of nanotubes across the whole 50 mm diameter wafer, with low size dispersion (~5%) when going from the center of the wafer to its edge This fabrication technology can be scaled up to 100 mm on any wafers or LED structures
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